1. Field of the Invention
The present invention relates to an ultraviolet laser-generating device, generating an ultraviolet laser beam or ray to be used for inspection or observation of minute pattern defects, foreign matters, etc., in the fabrications of, such as, semiconductor devices and a flat panel display, representatively, and further relates to a defect inspection apparatus and a method therefor, with using the ultraviolet laser ray obtained therefrom, thereby enabling detection of defects with high resolution, as well as a method for maintenance thereof.
2. Description of Prior Art
For example, circuit patterns formed on the semiconductor devices tends to be fine or minute, more and more, as the technology advance in the high integration thereof. In particular, masks and reticules, used in a process of photolithography for manufacturing of the semiconductor devices, as well as the defects of the patterns on a wafer, on which such as the circuit patterns of those are transcribed through exposure, are required to be detected with such the increasing high resolution. As a method for increasing the resolution, there can be listed up a way of shortening the wavelength of an illumination light from region of visible lights to that of ultraviolet lights. Conventionally, as a light source was used or applied, such as a mercury lamp, a Xenon lamp, etc., and only the light having a required wavelength(s) is/are selected optically from the various bright lines (or emission lines) of the lamp, to be applied thereto.
However, for the bright lines of the lamp, there are problems that it is difficult to compensate chromatic aberrations of an optic system due to wide range or width of the emission spectrum thereof, and that the light source comes to be large in size so as to obtain sufficient intensity of illumination, so that it has a bad or low efficiency, etc. In recent years, an exposure apparatus has been developed, installing a light source, KrF eximer laser of 248 nm in wavelength, as a light source thereof for use in manufacturing of the semiconductors, however there are also problems that the eximer laser ray source comes to be large in size thereof, and that it necessitates a certain countermeasure since it uses a fluorine gas therein, etc. Because of this, as the light source of such the ultraviolet (UV) laser ray other than the above-mentioned, YAG laser beam is converted in the wavelength by means of a non-linear optical crystal, thereby obtaining the third (3rd) high harmonic (355 nm) or the fourth (4th) high harmonic (266 nm) therefrom.
A wavelength converter device, obtaining the UV laser ray in this manner is already known by, such as, Japanese Patent Laying-Open No. Hei 8-6082 (1996)  less than prior art 1 greater than , Japanese Patent Laying-Open No. Hei 7-15061 (1995)  less than prior art 2 greater than , Japanese Patent Laying-Open No. Hei 11-64902 (1999)  less than prior art 3 greater than , and Japanese Patent Laying-Open No. Hei 11-87814 (1999)  less than prior art 4 greater than .
In the prior art 1 is described the wavelength converter device, comprising: resonance means, being positioned at an exit side of a light emission means for emitting a light having basic wavelength, having a resonance frequency corresponding to a resonance length, which is obtained by setting the length of an optical path, through which the light propagates, as said the resonance length, and a plural number of reflection means for reflecting said light in an inside thereof; a non-linear optical material, being positioned on the optical path of the light propagating through the inside of said resonance means, having an anisotropic property therewith, and for emitting the light being incident thereupon and at least one light converted in wavelength, being different from said light in the wavelength thereof; and an electric field applying means for applying an electric field to said non-linear optical material, so that the resonance frequency of said resonance means is in synchronism with the light of said basic wavelength, thereby generating the UV laser ray.
Also, in the prior art 2 is described the wavelength converter device, comprising: a light source for supplying a laser ray; an optical resonator for resonating a laser ray generated from said light source; a non-linear optical material, being positioned within said optical resonator, for converting the laser ray into a light wave having wavelength which is shorter than that thereof; and an optical system for feeding back said laser ray emitted from said optical resonator to said light source via the optical resonator, again, wherein said optical resonator, said non-linear optical material and said optical system are disposed within a vacuum container.
Also, in the prior art 3 is described the wavelength converter device of an outer resonation type, wherein, in a space defined between a wavelength converter element (for example, a non-linear optical crystal) and an optical member for separation of the laser ray (for example, a mirror having wavelength selectability therewith) is provided a material, which is optically transparent, or it is filled up with air or inactive gas, etc., or is kept into a substantial vacuum condition, so as to cut off or insulate a portion defined between said wavelength converter element and the optical member for separation of the laser beam, from an outside, there by preventing dusts and/or gas components from adhering and/or deposing on a light emission surface for the laser ray of said wavelength converter element and/or a light receiving surface of said optical member for separation of the laser ray.
And, the prior art 4 also describes an extension or prolongation in lifetime of the laser resonator, by removing contaminating materials, such as oil, etc., adhered on the mirror, which constructs the laser resonator, and/or on the component of the non-linear optical crystal, substantially.
However, in the wavelength converter device, a very little amount of active gas, generated when the ultraviolet light is incident upon the optical members, such as, all of the mirrors, etc., which are provided within the optical resonator, or upon the surface of the non-linear optical crystal, and when it is incident upon suspended or floating matters staying behind within the optical resonator, adheres upon the surfaces of the optical members, such as the mirrors, etc., and/or the non-linear optical crystal, later, thereby bringing about a problem of decreasing the permeability thereof, etc.
For dissolving such the problems, according to the prior art 2 mentioned above, the optical resonator, the non-linear optical material and the optical system are disposed within the vacuum container. However, since the optical resonator, the non-linear optical material and the optical system are disposed within the vacuum container, according to the prior art 2, though it is possible to protect the optical resonator, the non-linear optical material and the optical system from the contamination thereof, it is necessary to make the vacuum container secure so that no deformation due to internal stress will occur the inside of the optical resonator, the non-linear optical material and the optical system, as well as to make a seal construction certain. As a result thereof, it has a drawback that the vacuum container comes to be complex in the structure thereof, including the seal construction thereof, etc. Further, according to the prior art 2, as described in the Japanese Patent Laying-Open No. Hei 7-15061 (1995), there is a necessity of controlling the increasing temperature of the non-linear optical crystal, and because of this, heat fills up inside the vacuum container, therefore it has a drawback of giving an ill influence upon the optical member(s), such as other mirror(s), etc.
Also, in the prior art 3 mentioned above, the consideration was paid onto prevention of the dusts and/or gas components from adhering and/or deposing on the light emission surface of the laser ray of said wavelength converter element and/or the light receiving surface of said optical member for separation of the laser ray, by cutting off the portion defined between the wavelength converter element and the laser beam separation optical member from the outside, however no consideration was made upon prevention of adhesion or attaching of contaminating materials (contaminants) onto the optical resonator as a whole, including such the non-linear optical crystal, etc.
As explained in the above, any one of those prior arts 1 to 4 pays the consideration upon prevention of adhesion or attaching of the contaminants onto the optical resonator, as a whole, including the non-linear optical crystal, etc., with simplified construction thereof, but without receiving the ill influence so much from the control of increasing temperature of the non-linear optical element (i.e., the non-linear optical crystal).
An object of the present invention is, for dissolving such the problem(s) as mentioned above, to provide an ultraviolet laser-generating device, being simple in the structure thereof and able to convert the laser ray entered into with superior efficiency, with preventing adhesion or attaching of the contaminants on the whole optical resonator, including the non-linear optical crystal, etc., but without receiving the ill influence so much from the heat generated by the non-linear optical element, in particular, in the wavelength converter thereof, without decrease in intensity of an output of the ultraviolet laser ray, while obtaining a long lifetime thereof.
Also, other object of the present invention is to provide an ultraviolet laser-generating device and a maintenance method therefor, wherein an investigation can be made on a cause in the wavelength converter, when occurring the decrease in intensity of an output of the ultraviolet laser ray, thereby enabling to perform the maintenance thereof with ease.
Further, other object of the present invention is to provide a defect inspection apparatus and a method thereof, with using such the ultraviolet laser-generating device mentioned above, wherein microscopic test pattern formed on an object to be examined, such as the semiconductor wafer, etc., with an aid of illumination of stable intensity obtained by the ultraviolet laser ray, thereby enabling to examine the defects in the microscopic test patterns on the test object.
Also, further other object of the present invention is to provide a detect inspection apparatus and a method thereof, for achieving a long lifetime therewith, while can be maintained easily.
For achieving the above object(s) mentioned in the above, according to the present invention, in the ultraviolet laser-generating device, with paying an attention onto suppression upon potential of generating chemical gas reacted with residual organic matters, by irradiation of the ultraviolet laser ray within an optical resonator of the wavelength converter, the optical resonator is so constructed that no residual organic matter floats therein. In more details, the optical resonator and the non-linear optical element are provided within a container, hermetically, while replacing an inside of the container by an inert gas under the condition of preventing the organic matters from entering from an outside, so as to provide an environment where oxidation is reluctant to occur therein, as well as to prevent the heat due to isothermal control of the non-linear optical element from filling up therein, thereby preventing the ill influence of the heat upon other optical elements.
Namely, for accomplishing the above object(s), first of all, according to the present invention, there is provided an ultraviolet laser-generating device, comprising:
a laser ray source for irradiating and emitting a basic wave of laser ray therefrom;
a wavelength converter device for receiving the basic wave of laser ray emitted from said laser ray source and for converting it into an ultraviolet laser ray composed of a multiplied high harmonic light of the basic wave of laser ray; and
a container having an inlet window, upon which the basic wave of laser ray emitted from said laser ray source is incident upon, and an outlet window for emitting the ultraviolet laser ray composed of the multiplied high harmonic light of the basic wave of laser ray, and installing said wavelength converter device therein, wherein said container is filled up with an inert gas therein.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein said wavelength converter device comprises:
an optic resonator, being located within said container and constructed with plural optical members, for resonating the basic wave of laser ray; and
a non-linear optical element, being located within said container and constructed with plural optical members, for generating the ultraviolet laser ray composed of the multiplied high harmonic light obtained from the basic wave of laser ray.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein said container is hermetically sealed, and is further provided with means for discharging residual gas within said container and means for supplying the inert gas into said container.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein on a part of inner wall of said container is provided trap means for fixing contaminants floating within said container thereon.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein said container, in which said wavelength converter device is installed, is constructed in dual or triple construction, for defining an aperture between them, to be filled up with the inert gas therein.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, further comprising an optical detection means for detecting contamination condition within said container.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein said optical detection means comprises plural number of photoelectric conversion elements positioned within said container.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, further comprising a detection means for detecting an output intensity of the ultraviolet laser ray emitted from said wavelength converter device.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein said laser ray source comprises a solid-state laser-generating device.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein said laser ray source comprises a Nd:YAG laser and a wavelength converter for converting the laser ray from said Nd:YAG laser into a laser ray having xc2xd wavelength thereof.
According to the present invention, for accomplishing the above object(s), there is further provided a defect inspection apparatus for detecting defects in microscopic patterns formed on a test object, with using an ultraviolet laser ray, comprising:
an ultraviolet laser-generating device;
an illumination optical system for irradiating the ultraviolet laser ray emitted from said ultraviolet laser-generating device upon the test object;
an optical system for forming an optical image obtained from said test object, being illuminated by said illumination optical system;
a photoelectric converter for converting the optical image, which is formed by said optical system, into a signal upon receipt thereof; and
a defect detection circuit for detecting the defect on said test object upon basis of the signal obtained from said photoelectric converter.
Moreover, according to the present invention, for accomplishing the above object(s), there is also provided a defect inspection apparatus for detecting defects in microscopic patterns formed on a test object, with using an ultraviolet laser ray, comprising:
a plurality of ultraviolet laser-generating devices, being aligned so that the ultraviolet laser rays emitted are on a same axis;
an illumination optical system for irradiating the ultraviolet laser ray(s) emitted from at least one or more of said ultraviolet laser-generating devices upon the test object;
an optical system for forming an optical image obtained from said test object, being illuminated by said illumination optical system;
a photoelectric converter for converting the optical image, which is formed by said optical system, into a signal upon receipt thereof; and
a defect detection circuit for detecting the defect on said test object upon basis of the signal obtained from said photoelectric converter.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein at least one of said plurality of ultraviolet laser-generating devices is for a spare.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein said illumination optical system comprises an optical system for combining the ultraviolet laser rays emitted from each of said plurality of ultraviolet laser-generating devices, to illuminate the test object therewith.
Also, according to the present invention, there is provided the ultraviolet laser-generating device, as defined in the above, wherein said illumination optical system comprises a coherence reduction optical system.
Furthermore, according to the present invention, for accomplishing the above object(s), there is provided a method for inspecting defects in microscopic patterns formed on a test object, with using an ultraviolet laser ray, comprising the following steps:
generating an ultraviolet laser ray by the ultraviolet laser-generating device;
illuminating the test object with using the ultraviolet laser ray generated by said generating step;
forming an optical image of the test object from light obtained in said illumination step of the test object;
converting the optical image obtained in said forming step into a signal upon receipt thereof; and
detecting the defect on said test object upon basis of the signal obtained in said converting step.
Furthermore, according to the present invention, for accomplishing the above object(s), there is provided a method for inspecting defects in microscopic patterns formed on a test object, with using an ultraviolet laser ray, comprising the following steps:
generating a plurality of ultraviolet laser rays, so as to be aligned with on a same axis, as one ultraviolet laser ray;
illuminating the test object with using the one ultraviolet laser ray aligned in ed said generating step;
forming an optical image of the test object from light obtained in said illumination step of the test object;
converting the optical image obtained in said forming step into a signal upon receipt thereof; and
detecting the defect on said test object upon basis of the signal obtained in said converting step.
And, according to the present invention, for accomplishing the above object(s), there is also provided a method for maintaining the ultraviolet laser-generating apparatus as defined in the claim 8, comprising the following steps:
monitoring an output of the output intensity detecting means for comparing it to a certain value;
obtaining an output of said optical detection means for detecting contamination condition within said container of the ultraviolet laser-generating apparatus; and
determining maintenance of the ultraviolet laser-generating apparatus, upon basis of an output obtained by said obtaining step.